PROJECT SUMMARY Precise connections between synaptic partners are shaped during development to ensure proper neural circuit function, but how these connections are disassembled and rearranged after injury is less well understood. Glaucoma provides an excellent model to explore circuit plasticity when a postsynaptic neuron is injured. Furthermore, the ability to diagnose and treat glaucoma at an optimal stage before irreversible retinal ganglion cell (RGC) loss occurs requires a comprehensive understanding of inner retina circuit disassembly and plasticity. However, major gaps exist in knowledge about how RGCs are disconnected from and potentially rewired with their excitatory presynaptic partners, bipolar cells (BCs), how this remodeling affects RGC function, and the potential mechanistic role of microglia in circuit disassembly. Such knowledge is required to successfully develop optic nerve regeneration strategies that depend on functional circuit rewiring. The overall objective of this application is to determine the connectivity, function, and potential mechanisms of circuit disassembly and remodeling following intraocular pressure (IOP) elevation. The central hypothesis is that specific microcircuits in the injured adult retina may exhibit plasticity in terms of connectivity and function, with microglia playing an important role in synapse pruning. The hypothesis will be tested in the following specific aims: 1) Determine the specificity and timing of anatomic circuit rewiring in diseased adult retina; 2) Determine if diseased adult retina has the capacity for functional plasticity; 3) Identify the contributions of microglia in the mechanism of circuit disassembly. The approach includes biolistic transfection of individual RGCs, sub-micron imaging, electrophysiological measurements, and novel genetic tools to study bipolar-ganglion cell connectivity, RGC function, and microglia in experimental rodent glaucoma. The proposal is innovative because it examines the potential for cell-type specific rewiring, circuit-specific synapse pruning, and functional plasticity, concepts that shift the paradigm in understanding RGC degeneration in glaucoma. The proposed research is significant, because the resulting identification of both vulnerable and resilient retinal microcircuits to target will open new research horizons, particularly in novel psychophysics testing paradigms, drug development, and RGC regeneration or neuroprotection strategies. Finally, these experiments will fundamentally expand knowledge of how adult neural circuits react and rearrange in the face of injury.